CST PM & Calibration Schedules 3 — Questions and Answers
Question 1: A legal-for-trade retail scale must be re-verified after repair. Which agency in the United States has authority over weights and measures for commercial transactions?
- OSHA
- State Weights and Measures agencies (Correct answer)
- EPA
- USDA Food Safety Division
Correct answer: State Weights and Measures agencies
State Weights and Measures agencies, operating under authority derived from NIST HB 44, are responsible for regulating commercial weighing devices.
Question 2: What does 'eccentricity test' assess during a scale PM?
- The scale's resistance to electromagnetic interference
- The uniformity of the scale's response when a load is placed at different points on the platform (Correct answer)
- The speed at which the digital indicator updates
- The moisture resistance of the load cell housing
Correct answer: The uniformity of the scale's response when a load is placed at different points on the platform
An eccentricity (off-center load) test verifies that placing a load at different platform positions produces readings within tolerance.
Question 3: During a PM, a technician observes that a crane scale's hook and swivel show visible wear grooves. The technician should:
- Lubricate the grooves and return the scale to service
- Tag the scale out of service until the hook and swivel are replaced (Correct answer)
- Apply an increased safety factor in calibration
- File the grooves smooth and re-calibrate
Correct answer: Tag the scale out of service until the hook and swivel are replaced
Worn hooks and swivels are a safety hazard that can lead to catastrophic failure under load; the scale must be removed from service until repaired.
Question 4: ISO 9001 quality management systems require calibration records to be retained for how long?
- 6 months
- Until the device is sold
- As defined by the organization's own documented retention policy (Correct answer)
- Exactly 7 years per federal law
Correct answer: As defined by the organization's own documented retention policy
ISO 9001 requires organizations to retain calibration records as documented information but allows the retention period to be set by the organization's own procedures.
Question 5: A substitution weighing technique is used during calibration to reduce uncertainty. What is its main advantage?
- It eliminates the need for certified test weights
- It cancels systematic errors of the balance by comparing the unknown mass against a reference on the same pan in the same position (Correct answer)
- It speeds up the calibration process by 50%
- It allows calibration without removing the scale from service
Correct answer: It cancels systematic errors of the balance by comparing the unknown mass against a reference on the same pan in the same position
Substitution weighing places both the reference and unknown weights in the same pan position, canceling balance systematic errors and reducing uncertainty.
Question 6: A vehicle scale PM schedule calls for checking the 'approach and departure ramps.' Why is this important for calibration accuracy?
- Ramp condition affects aesthetic appeal
- Damaged or misaligned ramps can transmit side-loading forces to the weighbridge, causing errors (Correct answer)
- Ramp checks are only required for liability insurance
- Ramps affect the scale's electromagnetic shielding
Correct answer: Damaged or misaligned ramps can transmit side-loading forces to the weighbridge, causing errors
Misaligned or damaged ramps can apply horizontal forces to the scale platform, introducing errors not representative of the true vehicle weight.
Question 7: Which environmental condition documented during a PM could explain a scale consistently reading high in summer and low in winter?
- Power line voltage fluctuations
- Thermal expansion and contraction of the weighbridge structure affecting load cell preload (Correct answer)
- Increased humidity in summer only
- Changes in operator technique by season
Correct answer: Thermal expansion and contraction of the weighbridge structure affecting load cell preload
Thermal expansion and contraction of a scale's structural frame can change the mechanical preload on load cells, shifting calibration seasonally.
CST PM & Calibration Schedules 3
A legal-for-trade retail scale must be re-verified after repair.
Which agency in the United States has authority over weights and measures for commercial transactions?